A membrane-bound microsomal protein, which specifically binds p-aminophippurate (PAH) will be isolated using DEAE-sephadex column chromatography preparative disc electrophoresis, and gel filtration. The PAH binding protein and NMN (N'-methylnicotinamide) binding protein, previously isolated, will be characterized by SDS-gel and polyacrylamide-gel electrophoresis, and N-terminal analysis. The binding properties will be studies under various experimental conditions. Lipid and carbohydrate moieties are associated with the NMN binding protein, and possibly with the PAH binding protein; the lipid moiety will be identified by thin layer chromatography and the total carbohydrate determind. The amino acid composition, sub-unit molecular weight, size, and shape of both proteins will be determined. We will correlate binding and transport by comparing te properties of binding in purified plasma membranes to binding and transport in isolated dog renal tubules, includingthe usual kinetic parameters. To establish the role of intracellular trapping in the transport of organic ions, the renal cortes will be fractionated into its subcellular components by zonal ultracentrifugation, and the binding properties of NMN and PAH to each fraction determined. To facilitate the isolation and kinetic studies an affinity matrix for both NMN and PAH will be prepared. In addition, an antibdy to the NMN and PAH binding proteins will be produced to aid in correlating the role of the purified protein in transport.